deps: update dependency org.json:json to v20200518 (#239)

Author: renovate-bot

google-cloud-spanner/pom.xml

@@ -296,7 +296,7 @@
     <dependency>
       <groupId>org.json</groupId>
       <artifactId>json</artifactId>
-      <version>20190722</version>
+      <version>20200518</version>
       <scope>test</scope>
     </dependency>
     <dependency>